Acute liver failure and death due to the ingestion of normally therapeutic doses of acetaminophen (APAP), Tylenol, is a serious clinical problem in chronic alcoholics. The toxic response to APAP is hallmarked by hemorrhagic centrilobular necrosis and towering levels of serum transaminases which are preceded by centrilobular microvascular injury and congestion. Little is known about the pathophysiology of this early microvascular lesion, which is suspected to be important in the progression of magnitude of the subsequent parenchymal injury. We propose to study this aspect of the toxic response of the liver to APAP and its potentiation by alcohol bringing. The later is a growing and serious problem, especially on college campuses, but is pathophysiology has received little experimental attention. Preliminary data strongly suggests that alcohol binge drinking significantly increases the susceptibility of the liver to injury by APAP. The hypotheses to be tested in mice are: (a) APAP elicits alterations in the hepatic microvascular in a dose dependent manner that precedes and potentiates parenchymal injury and that alcohol bringing increases the susceptibility of the liver to injury by APAP; (b) that sinusoidal endothelial cells (SEC) and their cytoskeleton are the principal sites of microvascular injury; and (c) that injury to SEC is related to changes in their intracellular levels of glutathione (GSH) and cytochrome P450-2E1 (CYP2E1) as well as mediators released from Kupffer cells and/or recruited inflammatory cells. High-resolution in vivo microscopy will be used to determine the dynamic spatial and temporal development of hepatic microvascular dysfunction. Light and electron microscopic examination of fixed specimens and isolated SEC will elucidate structural alterations that can not ve visualized in vivo. These will be correlated with changes in GSH, CYP2E1, pro-inflammatory cytokines, superoxide, nitric oxide in SEC, liver and plasma to gain clues to explain the responses observed microscopically. How inhibition of these mediators modifies the injury will further elucidate their role. The results should provide new information about the pathophysiology and mechanisms involved in the early microvascular injury elicited by overdoses of APAP associated with suicide attempts or therapeutic doses of APAP in abusers of alcohol and their contribution to the time course, progression, and magnitude of hepatic injury. A better knowledge of the hepatic pathophysiology of alcohol bringing also should result.